1. Field of the Invention
The present invention pertains to oil and/or gas well operations. More specifically, it pertains to methods and apparatus used in performing wireline operations during the drilling, completion or workover of an oil and/or gas well.
2. Brief Description of the Prior Art
In conventional drilling operations, drilling proceeds through well hole or casing at the upper end of which is provided, near the surface of the well, a wellhead. Surmounted on the wellhead is a blowout preventer stack which usually includes an upper annular blowout preventer and one or more ram-type blowout preventers. Surmounted on the blowout preventer stack is a bell nipple assembly which terminates somewhere just beneath the rotary drilling table and the floor or platform of the drilling rig.
A string of drill pipe usually extends downwardly through the rotary drilling table, the bell nipple assembly, the blowout preventer stack and the wellhead down into the well. Drilling proceeds by rotating the drill string and the drill bit attached to the lower end thereof. Drilling fluids are usually introduced into the well through the drill string to control pressures in the well. However, in the event that pressure in the well should become excessive, the blowout preventers of the blowout preventer stack may be actuated to seal off the well to control these excessive well pressures. For example, the annular blowout preventer may be closed around the drill string to seal off the annulus between the drill string and the surrounding casing or hole.
At certain times during drilling, particularly during completion of the well or in workover operations, pipe string is removed and various types of wireline tools are lowered into the well suspended from a wireline or cable. This usually requires installation of a wireline lubricator assembly. The wireline lubricator is a device used, in conjunction with the drilling rig blowout preventers, to control pressure that may be encountered while performing various wireline services in cased or open hole operations. The lubricator assembly should be of sufficient size and length to totally contain the entire length and circumference of the wireline tool or tools being used. If well pressure is encountered while wireline operations are being performed, the wireline tools can be pulled up into the lubricator. Once the wireline tools are inside the lubricator, the blind rams of the ram-type blowout preventers are closed. The wireline tools and equipment can then be safely removed, the well pressure being contained below the blind rams.
The wireline lubricator assembly generally provides a tubular member which extends from somewhere near the blowout preventer stack upwardly through the rotary table and at the upper end of which is provided a wireline packoff assembly. The wireline tools are lowered through the lubricator assembly and a wireline pack-off assembly actuated or installed around the wireline to assist in controlling pressure in the well.
With one type of wireline lubricator, which may be referred to as the "flange-type", it is necessary to remove the bell nipple assembly. This requires unbolting of many bolts from the flange connection between the bell nipple assembly and the blowout preventer stack and the connection between the flowline and the bell nipple assembly. Then the bell nipple assembly is removed and the flange-type lubricator surmounted on the blowout preventer stack and bolted thereto. This bolted connection must be able to hold well pressure and requires testing for this purpose. After wireline operations are completed, then the flange-type lubricator assembly must be unbolted and removed and the bell nipple assembly reattached to the blowout preventer stack. Then the flowline must be reattached to the bell nipple assembly. While this type of lubricator assembly is relative safe, its use is very time consuming. The changing out of the bell nipple assembly and installation of the flange-type lubricator assembly may require several hours of rig time. Rig time is, of course, extremely expensive.
In an attempt to save rig time, a wireline lubricator of the "chained down" type has sometimes been used. This type of wireline lubricator does not require the removal of the bell nipple. In the chained down wireline lubricator, the tubular extension thereof is simply lowered through the rotary table and the bell nipple assembly. As this is initially done, the ram-type blowout preventer of the blowout preventer stack is closed while the annular blowout preventers remain open. The wireline lubricator is lowered until it makes contact with the blind rams of the ram-type blowout preventer. Then the wireline lubricator is picked up one or two feet above the rams and slips are set around the lubricator at the rotary table. Then chains are tied around the wireline lubricator above the rotary table and the chains are fastened to the rotary table or the rig floor. Thus, the only thing which prevents this type of wireline lubricator from being blown out of the well by excessive well pressures is the chains by which it is tied. While the chained down type wireline lubricator is relatively fast to install, it is far from safe. Few drilling companies are using the chained down type lubricator because of the hazards involved in its use.
In U.S. Pat. No. 4,553,591, apparatus is disclosed which eliminates the need to remove the bell nipple assembly for wireline operations. This apparatus includes a spool member which is installed between the blowout preventer stack and the bell nipple assembly. The spool may receive the mandrel of a test assembly for testing the seals of the blowout preventers or it may receive another mandrel of a lubricator assembly for wireline operations. In either case, the mandrels are seated within the spool member and peripherally sealed in the spool. They are retained in place by threaded radial pins. While this apparatus offers advantages over some of the prior art, it too has problems. For one thing, the number of pressure containing points is substantially increased. The spool requires a seal at its lower flange with the blowout preventers. In addition, there is at least one set of lock screws which must hold pressure. Pressure integrity is, of course, very important in drilling, completion and workover operations.
While the prior art has provided a number of ways of installing a lubricator assembly for wireline operations, the prior art designs are not totally satisfactory. Thus, the improvement for wireline operations continues.